1. Field of the Invention
The present invention relates to a four-wheeled electromotive cart with two front wheels and two rear wheels where the front wheels are driven via an electric motor.
2. Description of the Related Art
With present-day widespread use of vinyl plastic hothouses, melons are being widely grown even in cold-weather districts. In such vinyl plastic hothouses, which may be as large as 50-100 m in length, to anticipate a rich harvest, fertilization, transplantation of seedlings and crop harvesting is done by manual labor, only to a limited degree, and hence a high amount of mechanical assistance. So far, agricultural work in the vinyl plastic hothouses has been done using tractor, cultivator, etc. as the mechanical assistance, but these machines are not satisfactory from the viewpoint of working environment because their power source is an internal combustion engine (gasoline or diesel engine), and the hothouses become filled with exhaust gas from the engine. Also, because the tractor and cultivator are fundamentally agricultural machines for outdoor work, they are not easily handled in vinyl plastic hothouses of relatively small area.
To provide a solution to the foregoing inconveniences, a four-wheeled electromotive cart is proposed in Japanese Utility Model Publication No. 51-31502. The proposed electromotive cart generally comprises a front left wheel driven by a first electric motor via a chain wound around sprocket wheels, a front right wheel driven by a second electric motor via a chain wound around sprocket wheels, left and right rear wheels, and two batteries disposed between the front wheels and the rear wheels. By a user or human operator actuating two switches provided on a handle of the electromotive cart, the first and second electric motors can be controlled independently of each other to thereby allow the cart body to make turns as desired by the operator. The electromotive cart is very advantageous in that it does not produce exhaust gas. However, because the left and right front wheels are independently driven by the first and second motors, its capability to make turns or directional changes renders its linear movement very difficult, so that either a dedicated control device or the operator's experienced handling is required to control the left and right wheels to rotate at a same rate for the smooth linear movement of the cart.
In view of the foregoing, an improved four-wheeled electromotive cart is proposed in Japanese Patent Publication No. 53-4294, which is designed to reliably provide linear movability even on an agricultural road or on narrow, unlevel ground between furrows in a field. In this agricultural electromotive cart, the front wheels are driven by a single electric motor via belts, pulleys, chains and sprocket wheels, and the rear wheel axle has opposite ends bent at appropriate angles to provide toe-in and camber angles of the rear wheels so that linear movement of the cart is ensured on unlevel ground.
However, in the above-mentioned conventional four-wheeled electromotive carts employing belts, chains and sprocket wheels for transmission of the motor force, considerable jolts or shocks and difference in start timing between the left and right front wheels is caused by start of the motor rotation, due to a sudden stretch of the chains and a slip of the belts. In addition, due to the fact that the "front-wheel tread" is the same as the "rear-wheel tread", circling or turning movements of these carts tend to be of relatively large radius and require relatively great operating force by the human operator. Thus, with the arrangements of these conventional electromotive carts, it is difficult for the human operator to manually make small turns or directional changes of the cart.
The electromotive cart disclosed in the No. 51-31502 utility model publication has another drawback in that outer surface portions of the two batteries projecting beyond the outer side surfaces of the front wheels could damage farm products in the course of agricultural work.
Generally, the movement of the electromotive carts is subject to various limitations in carrying out agricultural work in a large-scale vinyl plastic hothouse, and hence it may be said that a lighter weight cart body is more preferred because it permits an easy directional change of the cart through manual operation of the human operator. However, with the electromotive cart disclosed in the No. 51-31502 utility model publication, which is driven via the two electric motors and designed to make directional changes by changing the respective directions of the left and right front wheels, desired directional changes of the body are difficult to make manually due to too heavy overall weight of the cart.
The No. 51-31502 utility model publication and No. 53-4294 patent publication show nothing about a harness unit electrically connecting the batteries and the electric motors, switches, etc. However, generally, if such a harness unit is attached to the body framework, the distance between the harness unit and the ground is small, so that splashed muddy water from the ground adheres to the harness or flicked pebbles from the ground would seriously damage the harness.